Phonograph pickup device



Dec. 9, 1947. B, ROBERTS 2,432,444

PHONOGRPH PICK-UP DEVICE Filed June 29, 1944 Patented 4Dec. 9, 1947 PRONO GRAPH PICKUP DEVICE Bruce Roberts, Philadelphia,'Pa., asslgnor, by mesne assignments, to Philco Corporation, Philadelphia, Pa., a corporation of Pennsylvania Application June .29, 1944, Serial No. 542,678 p 11 Claims. l

This invention relates to phonographic pick-up devices and more particularly to a novel pick-up of the capacity or condenser type.

One object of the invention is to provide a capacity type pick-up which is so constructed as to minimize the need for amplification of the generated signal. To this end the invention provides a capacity type pick-up in which the condenser elements or aplates are located very close to oneanother, so that the variations of capacity, due to .vibratory movement of one element, represent a large proportion of the normal capacity. Consequently, the variations of the capacitive reactance represent a large proportion of the normal reactance.

Another object of the invention is to provide a capacity type pickeup of this character which is readily capable of economic manufacture, and which requires no precision machined parts and no difiicult fitting of parts in assembly.

A further object of the invention is to provide a novel compliant mounting between the pick-up unit and its. associated tone arm, -whereby to effect a desired low frequency cut-off and to prevent tone arm resonance.

Other objects and features of the invention will be apparent from the following detailed description in connection with the accompanying drawing, in which:

Fig. 1 is a perspective view of the novel pick-up device in association with a record;

Fig. 2 is a perspective illustration of the pickup unit and the associated compliant mounting therefor;

Figs. 3 and 4 are perspective illustrations of the parts of the pick-up;

Fig. 5 is a sectional view taken along line 5-5 o1 Fig. 2;

Fig. 6 is a sectional View taken along line 6-6 v of Fig.2;

Fig. 7 illustrates in perspective the stylus de vice forming a part of the pick-up; and

Fig. 8 is a perspective View of an alternative form of the stylus device.

Referring first to Fig. l, there is shown a tone arm I carrying the pick-up unit 2, whose stylus 3 is in engagement with a record 4 on a turntable 5. The tone arm I is preferably of inverted channel form, and disposed within the end portion thereof is a compliant body or member I, which may be formed of rubber or other suitable compliant material. A clamping plate'l is adjustably secured to the tone arm by means of a screw 8 and serves to retain the compliant member 6 and also to vary the compliance thereof in accordance with thev adjustment of screw to adjustment of'the screw 8. A plurality of contact receptacles II'I are embedded ln the compliant member 6, as shown in Fig. 2, and are adapted to receive contact prongs II, which are provided on the pick-up unit 2. By means of this arrangement, the pick-up unit is removably attachable to the tone arm through the compliant mounting member 6. The compliant mounting of the pick-up unit will be discussed further hereinafter following the detailed description of the pick-up unitthe construction of which constitutes the principal feature of the invention.

As shown in Figs. 2 to 6, the pick-up unit 2 comprises a pair of outer insulating members I2 and I3 and an inner metallic member I4, the latter being "sandwiched between the two outer members when the pick-up is assembled. In Fig. 3, the members I2 and I4 are shown in a manner to illustrate their construction and Cooperative assembly, while in Fig. 4 the members I3 and I4 are shown in a manner to illustrate their cooperative construction and arrangement.

Referring to the metallic member I4, as best illustrated in Figs. 3 and 4, this member serves to support a thin iiexible metallic strip I5 which extends longitudinally of member I4 on one side thereof, and the end portions of which are secured to member I4 by means of attachment screws I6-II. It will be seen that one end of the strip I5 extends about an end of member I4 to the opposite side of said member, while the other end of the strip extends through an opening I8 in said member to the opposite side thereof. The strip I5 constitutes the movable element of the condenser and its intermediate portion is adapted to be vibrated by a stylus device I B secured to said portion. To permit such vibration of strip I5, its supporting member I4 is recessed at 20, it being understood that the depth of rccess 20 is not critical, since incidental capacity variations between member I4 and strip I5 are not utilized. `The strip is held taut and at by means of a wedgeV 2l seated in a recess 22 of member I4 and adjustably secured to said member yby means of screws'23. Thus, the strip I5 is maintained perfectly nat in engagement with the faces 24--25 of member I4 and in spanning relation to the recess 2.0. As shown in Fig..4, the outer in- 3 sulating member I3 is recessed to accommodate the aforementioned screws when the parts are secured together in assembled relation.

The insulating member I2 is adapted to freely.

support a rigid metallic element 26 which constitutes the other element or plate of the condenser. To this end, the member I2 is recessed at 2l so as to seat the element 2S. A bowed spring member 28 is disposed within the recess 21 and serves to urge element 26 toward the strip I when the parts are assembled. A very small space is maintained between the condenser elements I5 and 26 by thin insulating sheets 23 30, which are adapted to be interposed between the portions of said elements adjacent the faces 24 and 25. These sheets 28 and 38 constitute the sole elements which determine the spacing between strip I5 and the other condenser plate 25. It will be appreciated that the thickness of these spacers may be readily, and economically, held within the necessary close tolerances.

The metallic member I4 is provided with a contact prong 3I which is electrically connected to the vibratile ribbon I5 through the supporting member I4. Insulating member I2 is also provided with a contact prong 32 which is connected to spring member 28 through a connection 33. Thus, the prong 32 is electrically connected/to element 26 through the engagement of thevlatter with the spring member 28. l An insulating sheet 34 is adapted to be disposed in a recess 35 of member I2 which receives the projecting part of wedge 2|.

The stylus device I9 is pivotally carried by member I4 and projects through an opening 3B (see Fig. 2) formed by recesses in members I2 and I4. As shown in Fig. 7, thev stylus device comprises a stylus holder 3l having laterally extending arms 38 with spaced parallel extensions 38a which seat in cylindrical recesses 39 provided in the member I4 so as to pivotally support the stylus carrier. Raised portions I2a and I2b of member I2 are adapted to a'but the lateral arms 38, thereby holding the stylus securely while permitting the desired small rotational movement about said arms. The stylus also has an upwardly projecting finger 40 which is secured to the rear face of strip I5, for example by means of a suitable adhesive cement shown at 4I. Member I4 is recessed to accommodate the stylus carrier as illustrated in Figs. 3 and 4. At its lower end the stylus carrier has a laterally extending arm 42 which carries the stylus 3. The arrangement is such that lateral movement of the stylus, in response to lateral cut undulations of a record groove, effects pivotal movement of the stylus carrier about the pivot arms 38, so as to vibrate the exible strip I5 in relation t0 element 26. By virtue of the spring arm 42 the stylus may recede into the pick-up housing or casing, thus preventing injury to the stylus in the event that the pick-up is accidentally dropped. The parts of the pick-up are held in assembled relation by means of fastening screws such as shown at 43 in Fig, 6.

It will be seen from Figs. 5 and 6 that the adjacent surfaces of the condenser elements I5 and 26 are very close to one another, but accurately spaced by virtue of the aforementioned insulating spacing members 29 and 30. The spacing of condenser elements I5 and 26 is, of course, of magnitude sufcient to accommodate the maximum strip displacement encountered in practice. It will be noted from Fig. 6 that the stylus device I9 operates as a lever to effect the vibrations of 4 strip i5 in response to lateral movements of the stylus.

By means of the contact prongs on the pickup unit, the latter is removably attachable to the associated tone arm, as previously indicated. In the interest of better securement of the pickup unit and also to provide a balanced structure, a dummy prong 44 is provided on member I3, and a corresponding dummy receptacle is provided on the tone arm.

An alternative form of stylus device is shown in Fig. 8. In this instance the stylus carrier 31a is formed similarly to that above described but instead of having a laterally-extending stylus arm, the carrier serves to support a folded spring member 45 having upwardly extending arms 46 which are secured to the carrier 31a. The stylus 3a is supported centrally of the folded spring 45, as illustrated. In this instance the stylus is retractable by reason of its mounting on the spring member. This form may be employed in instances where the torsional compliance of laterally extending arm 42 is not required. The alternative form (Fig. 8), due to its lesser compliance, effects greater strip movement for a given needle displacement.

From the foregoing description, it will be seen that the invention has provided a capacity type pick-up of such construction that the parts can be easily manufactured and assembled, and in which the condenser elements may readily be brought into very close relation, so that the capacity variation attained represents a large proportion of the normal capacity. Consequently, when the present invention is employed in combination with an oscillator to produce a frequency-modulated cai'rier signal, very high carrier frequency deviations will be obtained. A typical F. M. phonograph pick-up is disclosed and claimed in United States Patent No. 2,322,621, issued June 22, 1943. It will be understood of course, that the pick-up may be employed in any instance where it is desired to produce a signal by means 0I capacitive reactance variations.

With regard to the compliant mounting of the pick-up, as hereinbefore described, such mounting further improves the operation of the pick-up by effecting a desired low frequency cutoi and by preventing tone arm'resonance. By providing a compliance of proper value between the pick-up and the tone arm, the low frequency cut-oilD can be made to occur at a selected point in the frequency response range. The compliant mounting illustrated affords a simple means for controlling the low frequency response. Moreover, the adjustability of the compliance by means of screw 8 enables accurate adjustment of the cut-off point.

While a single embodiment of the invention has been illustrated and described, it will be understood that various other embodiments and modifications may be resorted to within the scope of the invention as defined in the appended claims.

I claim:

1. A phonograph pick-up of the capacity type. comprising a three-part supporting structure or casing including two outer insulating members and a metallic member adapted to be interposed between said outer members, means for removably securing said members together,4 a flexible metallic strip having its end portions removably secured to said metallic member, said metallic member being formed to permit vibration of the intermediate portion of said strip, a stylus consecured to said metallic member, said metallic member being formed to permit vibration of the intermediate portion of said strip, means for l maintaining said strip taut and flat, a stylus connected to said intermediate portion to vibrate the same, a rigid conductive element freely supported by one of said outer members, resilient means urging said element toward said strip, and thin insulating means for maintaining said element in closely spaced reiation to said strip, said rigid element and said strip constituting a condenser whose capacitance is varied by the vibration vof said strip.

3. A phonograph pick-up' of the capacity type, comprising a three-part supporting structure or casing including two outer insulating. members and a metallic memberadapted to be interposed between said outer members, means for removably securing said members together, a ilexible metallic strip having its end portions removably secured to said metallic member, said metallic member being formed to permit vibration of the intermediate portion. of said strip, a stylus connected to said intermediate portion to vibrate the same, a rigid conductive element removably supported by one of said outer members in closely spaced relation to said strip, said rigid element and said strip constituting a condenser whose s capacitance is varied by the vibration of said strip,

a terminal prong on said metallic member, said prong being electrically connected to said strip through the metallic member, and a terminal.

members having a recess adjacent to said strip, a rigid metallic element freely supported in said recess, resilient means in said recess urging said rigid element toward said strip, insulating means,

arranged to prevent contact between said strip and said /element and to establish a predetermined spacing therebetween, and a stylus connected to the intermediate portion of said strip to vibrate the same.

7. In a phonograph pick-up of the capacity type, a pair of support members secured together in juxtaposed relation, a flexible metallic strip having spaced portions secured to one of said support members, said one support member being formed to permit vibration of an intermediate portion of said strip, an adjustable wedge carried by said one support member and engaging'said Astrip to maintain it taut and flat, a rigid metallic element carried by the other support member adjacent to said strip, insulating means arranged to prevent contact between said strip and said element and to establish a predetermined spacing therebetween, and a stylus connected to the intermediate portion of said strip to vibrate the prong on said one outer member and electrically connected to said rigid element.

4. A phonograph pick-up device, comprising a tone arm, a compliant body carried within the end portion of said tone arm, an adjustable pressure plate carried by said tone arm and engaging said body to vary the compliance thereof, a plurality of contact receptacles carried by said member, and a pick-up unit having contact prongs insertable in said contact receptacles for removable attachment of said pick-up unit to said tone arm through said compliant member.`

5. A phonograph pick-up device, comprising a tone arm, a compliant body carried within the end portion of said tone arm, an adjustable pressure plate carried by said tone arm and engaging said body to vary the compliance' thereof, a pickup unit, and inter-engaging contact means on said compliant member and said pick-up unit for effecting electrical connection to the pick-upunit and for removably attaching said unit to said tone arm through said compliant member.

6. In a phonograph pick-up of the capacity type, a pair of support members secured together in juxtaposed relation, a flexible metallic stripl having spaced portions secured to one of said support members, said one support member being formed to permit vibration of an intermediate same.

8. In a phonograph pick-up of the capacity type, a support structure including a metallic member, a relatively narrow exible metallic strip having spaced portions secured to said member and a vibratile portion intermediate said spaced portions, said member being recessed to permit vibration of the intermediate portion of said strip, said member also having a recess adjacent one of the secured portions of said strip, a wedge extending transversely across said strip in cooperative relation with said recess, means for drawing said wedge into said recess to render the intermediate portion of said strip taut and perfectly fiat, a rigid flat-faced metallic member held 'by said support structure in very close relation to the intermediate portion of said strip, and a stylus connected to the intermediate portion of said strip to vibrate the same.

9. In a phonograph pick-up of the capacity type, a pair of support members secured together in juxtaposed relation, a ilexible metallic element supported by one of said support members in confronting relation with the other support member, said element having spaced portions secured to said one support member, the latter being vformed to permit vibration of an intermediate portion of said element, said other support member having a recess adjacent to said element, a rigid metallic element freely supported in said recess, resilient means in said recess urging said rigid element toward said flexible element, insulating means arranged to prevent contact between said elements and to establish a predetermined spacing therebetween, anda stylus connected to the intermediate portion of said flexible element to vibrate the same.

10. In a, phonograph pick-up of the capacity type, a pair of support members Secured together in juxtaposed relation, a flexible metallic element supported by one of said support members in confronting relation with the other support member, said element having spaced portions secured to said one support member, the latter being formed to permit vibration of an intermediate portion of said element, an adjustable wedge carried by said one support member and engaging said element to maintain it taut and ilat, a rigid metallic element supported by said other support member adjacent to said flexible element, insulating means arranged to preventI contact between said elements and to establish a predetermined spacing therebetween, and a stylus connected to the intermediate portion of said flexible element to vibrate the same.

11. In a phonograph pick-up of the capacity type, a pair of support members adapted to be secured together in face-to-face relation, a exible metallic strip extending along the face of one.

of said support members, the ends of said strip extending to the opposite side of said one support member and being secured thereto, an adjustable Wedge on the face of said one support member engaging said strip to Akeep it taut and flat, said one support member being formed to permit vibration of the intermediate portion of said strip, a rigid metallic element carried by the other support member adjacent to said strip, insulating means arranged to prevent contact between said strip and said element and to establish a pre-determined spacing therebetween, and a s stylus connected to the intermediate portion of said strip to vibrate the same.

BRUCE ROBERTS. 

